MS Thesis Presentation by John Lyle Fouts
Friday, December 16, 2005
(Dr. Cyrus Aidun, Chair)
"Forming Screen Effect on Ultrasonic Beam Field"
The aim of this study was to characterize the interaction between a pulsed ultrasonic wave and a paper forming screen. Ultrasonic signals were analyzed to determine the ultrasonic beam echo amplitude and shape. The signal was transmitted and received using four different ultrasonic transducers: a 2 MHz 10 mm, 4 MHz 5 mm, 4MHz 8 mm focused, and 8 MHz 5 mm. The 4 MHz transducer turned out to represent a good tradeoff between the high attenuation of the 8 MHz transducer and the low resolution (measurable depth and velocity) of the 2 MHz transducer. These tests were performed with and without various paper forming screens placed between the ultrasonic transducer and an ultrasonic signal target.
Two different paper forming screens were utilized to study the interaction of the ultrasonic beam with the forming screens. The tests showed that the ultrasonic signal passing through the forming screens is greatly attenuated causing a sharp decrease in echo amplitude. To overcome the attenuation of the signal, a much higher amplification of the signal was used causing an increase in the saturation region around the forming screen. General trends such as beam convergence just past the forming screen and then divergence were seen throughout the forming screen tests, but all tests seemed to have some amount of variation. An experiment was produced that could test for the variation in the lateral movement of the forming screen in the water bath. The tests also show that even though the pores in the forming screen are very small, they seem to have a great effect on the beam width measurements of the ultrasonic transducer.